An automatic transmission shifts by engaging and releasing friction elements. At the time of engaging a friction element, a shift shock occurs unless a control pressure is appropriately controlled. Accordingly, a learning control is generally performed to store a hydraulic pressure at the time of engagement and reflect a stored value at the time of a next control.
A control hydraulic pressure of the frictional engagement element can be appropriately controlled by this learning control.
Such a control is disclosed in JP10-331962A. In JP10-331962A, a deviation amount from a proper value of an initial hydraulic pressure command value Ci for obtaining the value of an initial hydraulic pressure supplied to a high-speed frictional element to be engaged after the elapse of a predetermined time following the start of upshifting is calculated using an evaluation index (maximum control deviation emax) based on a change in the rotation speed of an input shaft in a gear transmission at an initial stage of an inertia phase at the time of upshifting in a vehicle automatic transmission. A learning control is performed by setting an initial hydraulic command value at the time of next upshifting using the deviation amount.